When a person dies, the body loses the complex functions that maintain continence, which often results in the release of waste. This common observation has a straightforward physiological basis rooted in the immediate shutdown of the nervous system and the later process of biological decomposition. Understanding why this happens requires separating the instantaneous loss of muscle control from the delayed buildup of internal pressure.
Immediate Loss of Muscle Control
The body maintains continence through a coordinated system of muscles that seal the rectum and bladder. This control mechanism is instantly disabled at the moment of somatic death because muscle control relies on continuous signaling from the brain and spinal cord. When nerve activity ceases, the body enters primary relaxation or flaccidity, where all muscles lose their tone.
The anal closure system involves two structures: the internal anal sphincter and the external anal sphincter. The internal sphincter is smooth, involuntary muscle tissue, usually contracted and not under conscious control. The external sphincter is skeletal muscle, which is under voluntary control and can be consciously tightened.
At the moment of death, both sphincters relax completely because the nervous signals maintaining their contracted state are immediately halted. If fecal matter is present in the lower gastrointestinal tract, the lack of a muscular barrier allows gravity and existing internal pressure to cause immediate expulsion. This instantaneous relaxation is the most frequent cause of post-mortem release and is purely a mechanical result of the nervous system’s failure.
Delayed Release Due to Internal Pressure
A separate mechanism causing expulsion occurs hours or days after death and relates to biological decomposition. Once circulation and the immune system stop, the vast population of bacteria residing in the gut begins to multiply unchecked. These microbes start feeding on the body’s tissues, a process called putrefaction.
The bacterial consumption of organic compounds generates a significant volume of gaseous byproducts. This microbial metabolism produces gases like methane, carbon dioxide, and hydrogen sulfide. This gas accumulation causes the abdomen to become visibly distended and bloated, a phenomenon that begins around 24 to 72 hours after death, depending on environmental temperature.
The pressure created by these gases can be immense, turning the abdominal cavity into a pressurized chamber. This rapidly increasing internal pressure physically forces any remaining fecal matter out of the rectum. Since the sphincters are already relaxed from the initial flaccidity, the internal pressure acts like a piston, pushing the contents outward. This delayed expulsion is a secondary event driven by decomposition, distinct from the immediate muscular relaxation at the moment of death.